.the anoplasm is a very good conductor of electricity and The axoplasm is separated from another electrically very good conductor material,

neurilemma containing large number of phagocytes, digesting The ingested material. Such a tube is called a "ghost tube", a term coined by Edward Sharpey- Schafef B. Changes in The proximal part 1. The same degenerative changes are seen m The proximal stump, but only upto The node of Ranvier nearest to The injury 2 The cell soma also shows changes ll shows chromatolysis (degeneration of The Nissl granules) and some swelling. REGENERATION OF A DEGENERATED NERVE Provided there is a neunlemmal sheath, a degenerated nerve may regenerate In a case of satisfactory regeneration, the steps are as follows : 1 The axis cylinder from the proximal stump, grows and sprouts out from the cut end The emerging sprout may be branched [N B (a) In place, where the neunlemma is absent, there can be no regeneration Nerve fibers of The CNS therefore, once degenerated, never regenerate as these nerves hava no neurilemma (b) When a peripheral nerve fiber is inured regeneration occurs following The degeneration no doubt, but if the nerve cell body (soma) dies, no regeneration is possible (c) If an axon of the brain degenerates, there will be no regeneration, as staled above But in addrtion, retrograde degeneration occurs severely, ultimately causing the dealh of the soma As mentioned earlier, (chap l. sec.XA), owing to The absence of minosish such dead soma cannol be replaced by fresh nerve cells). 2 Provided the distance bet ween the proximal and the distal portions are not great h the sprout or a branch of The sprout, enters the 'ghost tube' and keeps on enlarging, at a rate little over 1 mm/day, tilt it reaches The terminal end and establishes connection with The motor end plate The cells of Schwann cause myelimation the axis cylinder. The growth of the axis cylinder 15 due to vigoros protein synthesis by The nerve cell body (soma). The newly synthesized protein travels into The axon APPLIED PHYSIOLOGY 1 If the gap between the cut ends of The nerve, that is. The distance beiween the proximal and peripheral slumps is great, eiceedrng 3 mm, regeneration r. difficull. because bridging of The gap by neuntemma becomes difficult Regeneration in such cases may be helped by surgical procedure (sutunngthe cut ends of the nerve). Such surgical procedures should be taken up quickly, otherwise the motor end plate may alrophy 2, The sprout emerging out of the proximal stump, in some cases, may expand and develop into a 'neuroma' In such cases, regeneration does not occur. Moreover, neuroma is a nasly surgical problem, causing intense pain and tends to recur ever) after removal A neuroma may be a complication of a surgical amputation of a limb 3 Degeneration of peripheral nerve fiber occurs not only due to injury, but may develop as a result of diseases, e.g leprosy (infestation of Schwann cell by lepra bacillus), diabetic neuropathy (a non infective degeneration of penpheral nerves in untreated diabetes) and so on Thus, diabetic neuropathy may lead lo severe hypotoma and weakness ol limbs/loss of jerks etc. etc. (all because, the axons supplying the muscles, are now lost). Proper treatment helps The neural regeneration ~> disappearance of the symptoms 4 As slated earlier regeneration does not occur in the nerves of CMS and in the optic nerve 'CABLE STRUCTURE' OF NERVE FIBER Imagine a nerve fiber which is nerther myelinated nor has a neunlemma Its axolemma (which ensheathes the anoplasm), therefore, is in contact with the ECF Both the ECF as well as the asoplasm are good conductors of electnciiy but The axolemma, which intervenes these two structures, is electrically resistant and acts as an insulator This arrangement is called a cable structure of nerve and many of The electncal properties of a nerve fiber owes its origin to such a cable structure However, normally a nerve fiber is covered by neurilemma. which complicates The picture The gap which is present between the neurilemmal membrane and the axolemma however can communicate with the ECF, though the communication probably occurs via tortuous channels In short, nerve fibers have cable structures, that is .the anoplasm is a very good conductor of electricity and The axoplasm is separated from another electrically very good conductor material, viz, the ECF by electrically nonconducting nerve membrane The deposition of myelm in myelinated nerve further complicates the picture In a myehnated nerve, the membrane overlying the nodes of Ranvier are good conductors but The nerve membrane, overlying the inlemodes are bad conductors This, essentially, is the basis of saltatory conduction, seen in myehnated nerve The term, cable, in This instance, means, insulated wires Recall, when a nerve fiber is conducting an impulse, it develops a current called action potential (AP) But this is also a fact that this AP does not spread laterally (ie. leak) from one nerve fiber to another Imagine what catastrophe would have happened then A small part of brain, once excited, would cause excitalion of The whole brain. because the APs produced in the local neurons, in absence of this cable structure, would leak and excite the neighbouring neurons. AXOWAL FLOW (AXON TRANSPORT) Many substances found mthe anon ate not synthesized by the axon. but are formed by The nerve cell body (soma). These substances then travel down the axoptasm. by a cen­trifugal (i) slow moving or a (n) fast moving How Proteins lhal are synthesized by The nbosomes of soma. move slowly, whereas The building materials (or The neurotransmitlers (e g acetyl choline) move fast. These are examples of axonal